Translation
(14) Fasting (Kitab Al-Siyam)
كتاب الصوم
(795) Chapter: Regarding The Allowance For That
(29) باب فِي الرُّخْصَةِ فِي ذَلِكَ
Sunan Abi Dawud 2375 
Narrated Anas:
We would not allow a man who was fasting to get himself cupped due to abomination of hardship.
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، حَدَّثَنَا سُلَيْمَانُ، - يَعْنِي ابْنَ الْمُغِيرَةِ - عَنْ ثَابِتٍ، قَالَ قَالَ أَنَسٌ مَا كُنَّا نَدَعُ الْحِجَامَةَ لِلصَّائِمِ إِلاَّ كَرَاهِيَةَ الْجَهْدِ ‏.‏
Grade :  Sahih (Al-Albani) صحيح  (الألباني)حكم :
Reference : Sunan Abi Dawud 2375
In-book reference : Book 14, Hadith 63
English translation : Book 13, Hadith 2369